Dr. Cregg's chart assumes 5 to
6.5 gallons per minute from the garden hose. You can check the flow
rate from your hose by using an empty milk or water jug. Let
the hose run in the jug, and time it filling. Use a watch with a
timer or a second hand to get an accurate measurement.

Dr. Cregg also recommends avoiding runoff. Once you've measured your flow
rate, add a sprinkler, or soaker hose, or a hand-held watering wand to the
end of the hose. This breaks up the fall of water, and helps to reduce
runoff. You can even put out a small, straight-sided can to measure the
amount of water you're putting on, in inches.

Dig into the soil a little to check it before watering. If yours
is already moist, leave it alone! Your tree has water available to
it, and you can wait a day or three before watering.

Irrigation doís and doníts

Bert Cregg
Horticulture and Forestry, Michigan State University
Reprinted from MSU's
Landscape Alert 09-09-05(this link will take you to a web site outside trimpines.com)

For most of Michigan water needs in the landscape are reaching critical levels. Although showers are in the extended forecast, itíll take a few good day-long soakers to significantly affect soil moisture below the surface of the soil. While many homeowners are diligent to keep their lawns watered and green, trees and shrubs often get ignored. Reducing stress to trees and shrubs this time of year is critical. As we go into the fall trees are shifting internal resources and undergoing physiological changes that will enable them to withstand the rigors of the winter to come. If plants are subjected to severe stresses now, they will be more predisposed to various winter injuries. With this in mind, irrigating trees and shrubs should be on your list of landscape chores. Here are a few ďDoís and DonítsĒ to bear in mind as you irrigate your landscape.

do

Give good, long soakings rather than frequent light waterings. A typical rule of thumb is to provide at least 1 inch of irrigation per week. How many gallons of water this translates into depends on the size of the tree. If we measure the width of crown spread of a tree we can calculate the area under the drip line. We can then figure the volume of water needed to cover this area with 1 inch of water. Iíve done this in the table below and converted the volume to gallons. Iíve also calculated the length of time it would take to apply 1 inch of water assuming a typical garden hose flow rate of 5 to 6.5 gallons per minute.

Increase the irrigation of amount as temperatures soar. The 1 inch per week is a good rough guide but peak evaporative demand can approach 2 inches per week in Michigan during extremely hot summer weather.

Apply mulch properly. Mulching is the best way to conserve precious soil moisture in the landscape (See related article in this Landscape Alert.).

Use irrigation bags on newly established trees. Gator bags are designed to provide about 15 gallons of water over several hours, providing an easy way to ensure a slow steady watering.

Gallons of water needed to provide 1 inch of irrigation under the dripline of trees of various sizes

Tree crown spread (ft)

Gallons

Minutes of watering*

6

20

3 - 4

8

30

5 - 6

10

50

8 - 10

12

70

11 - 14

16

125

20 - 25

20

200

30 - 40

*Assuming 5 to 6.5 gallons per minute from typical garden hose

donít

Allow water to run-off. Water that runs off is wasted water. If youíre watering by hand and notice water running off move from tree to tree to allow water to soak in before resuming watering.

Ignore signs of drought stress in landscape plants. Wilting leaves, leaf scorch, dropping leaves and drooping leaders in conifers are your treeís way of saying, ďWhatís a guy gotta do to get a drink around here?!Ē

Water during hot midday periods to reduce water loss to evaporation. Some experts argue against watering late in the evening due to possible disease problems associated with wet foliage. Morning is the best time to water Ė unless you have to be at work.